Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROU~D OF l~IE I~VENTION
The present invention is concerned with a
bioreactor for the biochemical treatment of liquids
containing organic matter. The invention is more
particularly directed to a bioreactor suitable for the
fermentation of aqueous solutions of fermentable
sugars, such as bisulfite liquors originating from the
pulp and paper industry, to produce ethanol as a
valuable by-product.
The need to treat on a profitable basis the
bisulfite liquors from the pulp and paper industry is
becoming more and more urgent due to the pollution
regulations imposed by governments.
The annual world production of pulp by the
sulfite process is about 11.5 million metric tons on
dry basis, 1.5 millions of which originate from the
United-States and 2 millions from Canada. For each ton
of dry sulfite pulp produced, there is about one ton
of waste products in the form of solids dissolved in
zo water, a major portion of this bi~ulfite liquor being
dumped into rivers. Such a liquor has the following
t~ical composition:
% Total Solids
Lignosulfonate 52
25 Extractive matters 3
Poly and oligosaccharides 6
Monosaccharides 23
- galactose : 3
- glucose : 3
- mannose :11
- arabinose : 1 -~
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- xylose 5
Glucuronic acid
Aldonic acid 4
Sulfonated sugar 3
Acetic acid 2
Methanol
Calcium bisulfite 5
100/~
The production of ethanol by fermentation of
the sugars contained in the above liquor i5 of particular
interest since the ethanol can be readily separated
from the remainder of the liquid after fermentation.
The conversion rate of biochemical reactions, however,
is much more slow compared to the conversion rates of
pyrolysis or direct combustion reactions. Thus, on an
industrial scale, the use of a biochemical process
necessitates a bioreactor having a high productivity.
The productivity of conventional stirred tank
fermentors operated either continuously or disconti-
nuously is limited by the specific growth rate of themicroorganism cells. In a continuously operated tank-
type reactor, the substrate circulates continuously
through the reactor. When the medium is perfectly
agitated, the cell concentration is the same everywhere
in the reactor and the cells thus flow out of the reactor
together with the substrate at the same concentration as
in the reactor. An increase in the flow rate will
therefore dilute the cells in the reactor, resulting in
a lowering of the reactor productivity since the rate of
product formation is proportional to the num~er of
microorganism cells in the system. Thus, at a
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sufficiently high flow rate, the dilution rate will
exceed the specific growth rate of the cells correspond-
ing to the operating substrate concentration, causing
the so-called phenomenon of cell washout.
S On the other hand, various tubular bioreactors
have been proposed, such as the free-cell reactors with
or without cell recycle and the immobilized-cell
reactors. In the free-cell reactor without cell recycle,
the substrate and microorganism cells are introduced
at the same time into the reactor, that is, at the
beginning. Once the reactor is filled, the substrate
circulates through the reactor. The productivity of
this type of reactor is also affected by the same pheno-
menon of cell washout as in the continuously operated
stirred tank-type reactor. When such a free-cell reactor
is operated with cell recycle, it requires the additional
use of a centrifugal machine in order to accomplish the
cell recycle. This is not only expensive both in terms
of capital investment and subsequent operating costs,
but could also cause destruction of the cells. Moreover,
it has been observed that the specific rate of product
formation drops considerably as soon as the substrate
concentration falls below l0 g/l.
By immobilizing the cells inside the reactor,
using for instance a packing of gelatin coated ceramic
particles treated with glutaraldehyde, the reactor
can operate at a dilution rate exceeding the specific
growth rate of the microorganism cells. Although such
an immobilized-cell reactor has a productivity which
is considerably higher than that of a free-cell reactor
without cell recycle, it suffers from several disadvan-
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tages. Firstly, the film of gelatin which coats the
ceramic particles swells during operation, causing a
reduction of the nominal void percentage of the packing
to about 50-55%. In other words, the usable volume of
the reactor is only about 50% of the total real volume.
'rhe immobilization step is also very delicate and time
consuming and requires additional equipment. 'rhe
glutaraldehyde which serves to bind the cells to the
gelatin molecules further acts as a bactericide; thus,
too much glutaraldehyde could kill the im~nobilized cells
whereas too little would allow the gelatin to dissolve
in the flowing liquid to be fermented and thus cause a
rupture of the bonds by means of which the cells are
attached to the ceramic particles. me time required
to start the reactor, after having filled the latter
with the packing, disinfected the whole and inserted
the cell culture, is about 8 hours; however, one must
also consider the time required to recycle the packing
between two cycles of operation, which is about 48 hours,
Moreover, in the case of contamination, the packing
including the gelatin film must be completely regenera-
ted. Finally, there is a progressive dissolution of the
gelatin film, which reduces the quantity of immobilized
cells, thus resulting in a continuous lowering of the
reactor productivity as a function of the operating
time.
SUMMARY OF THE INVENTION
It is therefore an object of the present
invention to overcome the above drawbacks and to provide
a bioreactor having improved stability and productivity.
1240631.
It is another object of the invention to provide a
bioreactor for the biochemical treatment of liquids con-
taining organic matter, which enables the microorganism
cells to be retained inside the reactor without being
immobilized while still preven-ting the cells from being
substantially entrained by the liquid undergoing trea-tment.
In accordance with the invention, there is pro-
vided a bioreactor for the biochemical treatment of liquids
containing organic matter, comprising an elongated, upwardly
extending tubular container having inlet means for receiving
the liquid to be treated and outlet means for discharging
the treated liquid, and a plurality of spaced-apart first
and second trays with each of the first trays being arranged
alternatively with the second trays inside the container,
each tray being apertured to provide liquid flow commu-
nication between the inlet and outlet means and adapted to
support a respective bed of microorganism cells capable of
reacting with the organic matter. The apertures of the first
and second trays are arranged relative to one another to
cause the liquid to flow laterally across the respective
cell beds of the trays as the liquid flows from one tray to
another. The trays are sufficiently close to one another
such that upon reaction of the microorganism cells with the
organic matter, microorganism cells projected from a bed
supported by a respective one of the trays are deflected by
a tray located immediately above the respective one tray to
deposit back onto the bed of the respective one tray,
thereby substantially preventing the cells from being
entrained by the liquid flow.
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According to a preferred embodiment of the in-
vention, the apertures of the first and second trays are
arranged to provide a radial liquid flow across the
respective cell beds of the trays. For example, each first
tray can be formed with a single central aperture and each
second tray with at least two apertures arranged opposite
one another on either side of a central longitudinal axis
extending through the central aperture of each first tray,
whereby the liquid flows radially outwardly across the
respective cell bed of each first tray and then radially
inwardly across the respective cell bed of each second tray.
Preferahly, the second tray includes two pairs of such
opposite apertures, each pair being arranged in equi
distantly spaced relation to the other and positioned
adjacent a peripheral edge of the second tray.
According to another preferred embodiment, the
trays are removably mounted inside the container and spacer
means are arranged between the trays to maintain the trays
in spaced relation to each other. In order to allow the
trays to be readily removed from the container, the latter
is advantageously provided with a removable cover which is
releasably secured to the container at an upper extremity
thereof. A laterally outwardly extending flange may be
provided at the upper extremity of the container so as to
enable the cover to be releasably secured to the flange by
releasable fastener means.
In a further preferred embodiment of the in-
vention, an outer wall spacedly surrounds the container to
define therebetween an annular chamber adapted to contain a
thermostatic fluid for maintaining the liquid at a substan-
tially constant temperature.
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When the bioreactor of the invention is to be used
for carryinq out a fermentation process, it is first proper-
ly disinfected and then simply filled with a suspension of
the desired microorganism cells in sterile water at a
predetermined concentration, for example 30 g/l, by first
flowinq such a suspension througn the container and then
stopping the flow to cause the cells to deposit onto the
trays by sedimentation. The liquid
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,~c,,~ ~.
,
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to be treated can thereafter be fed to the reactor at a
flow rate of about 5 ~1/min., for example. Thus, the
starting time is limlted to the time required for filling
the reactor. In the case of contamination, the cells can
S be removed from the reactor by bubbling with an air
strea~ which creates a turbulence sufficiently high to
fluidize the cells and cause the latter to flow out of
the reactor without having to remove the trays-. Alterna-
tively, the trays can be removed through the top of the
reactor after having removed its cover, for thorough
cleaning and disinfection.
The bioreactor according to the invention
eliminates the immobilization step required in the case
of an immobilized-cell reactor, as well as all the
equipments associated therewith. Such an immobilization
step is replaced by a simple filling of the reactor with
a suspension of the cells in sterile water. Moreover,
the bioreactor of the invention does not necessitate
any material which could have a bactericidal-effect and
thus kill the cells.
In the bioreactor according to the invention,
the void percentage is defined by the thickness of the
trays, Since the liquid undergoing treatment does not
exert any mechanical strain on these trays, the thickness
of the trays can be reduced and the void percentage can
thus reach about 90%. Therefore, the usable volume of
the reactor tends toward the total real volume.
An agitation has been observed in the
liquid undergoing treatment in a bioreactor according to
the invention. This agitation occurs in regions whose
boundaries are defined by the upper surfaces of the cell
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beds and the lower surfaces of the trays, and it is
caused by the gas which is formed at the surfaces of the
sedimented cells as a result of the biochemical reaction
(e.g. fermentation or biodegradation). When a gas
bubble is liberated from the surface of a cell, a
portion of the sedimented cells is projected vertically
in the liquid. me cells bounce off the surface of a
tray immedlately located above and a majority of these
cells then deposit back onto t~e same tray. Thus, the
1~ multi-tray bioreactor of the invention can be considered
as defining a series of continuously stirred tank reactors
arranged in cascade, where each tray acts not only as a
mini-reactor containing a layer of active cells but also
as a cell separator preventing the cells from being
entrained by the liquid flow.
As mentioned previously, the bioreactor of the
invention is particularly useful for the anaerobic
fermentation of aqueous solutions of fermentable sugars,
such as mannose, glucose and galactose, which are con-
tained in bisulfite liquors originating from the pulpand paper industry, or other industries. It can also
be used for the biodegradation of effluents containing
biodegradable organic matter and may thus be useful in
the ~iotreatment of effluents from the cheese industry
for example, to reduce the chemical oxygen demand and
to produce methane which can be used in the cheese plant
to satisfy part of its energy requirement.
BRIEF DESCRIPTION OF THE DRAWINGS
Further features and advantages of the inven-
tion will become more readily apparent from the following
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description of preferred embodiments, with reference to
the accompanying drawings, in which:
Fig. 1 is a longitudinal sectional view of
a bioreactor according to the invention,
Fig. 2A and 2B are plan views of the two types
of trays utilized in the bioreactor of Fig. 1
Fig. 3 is a schematic flow diagram illustrating
how the li~uid flows through the bioreactor of Fig. 1,
Fig. 4 is a schematic diagram illustrating how
the bioreactor of Fig. 1 can be utilized for the bio-
chemical treatment of liquids containing organic matter:
Fig. 5 is a graph showing the conversion rate
of an aqueous solution of fermentable sugars as a func-
tion of the bioreactor length; and
Fig. 6 is another graph showing the removal
rate of the chemical oxygen demand (C.O.~.) from a-cheese
plant effluent as a function of the residence time in the
bioreactor. i
DESCRIPTIO~ OF PREFERRED EMBODIME~TS
Referring first to Fig. 1, there is shown a
tubular multi-tray bioreactor generally designated by
reference numeral 10 and comprising an elongated, verti-
cally-extending tubular container 12 of circular cross-
section having a base 14 and a removable cover 16. ~wo
types of planar trays 18 and 20 are alternatively arranged
above one another inside the container 12. The trays
18,20 are removably mounted inside the container in
spaced relation to each other by means of removable
spacers 22 consisting of ceramic cylinders arranged
between the trays; the spacers 22 can ~e fixed to either
the trays 18 or trays 20 and thus be removable therewith.
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As best shown in Fig. 2, the trays 18 and 20 are circular
with the tray 18 being formed with a single central aperture
24 and the tray 20 with two pairs of diametrically opposite
apertures 26 arranged in eauidistantly spaced relation to
S each other adjacent the peripheral edge 28, the apertures 24
and 26 being circular. In order to provide a constant liquid
flow through the reactor, the apertures 26 define a total
area which is substantially equal to the area of the
aperture 24.
The bioreactor 10 further includes an inlet 30 at
the base 14 for receiving the liquid to be treated and an
outlet 32 arranged in the cover 16 for discharging the
treated liquid. As shown, the base 14 comprises two plates
34 and 36, the plate 36 serving to mount the container 12.
The inlet 30 includes a conduit 38 extending through the
base plates 34, 36 and opening into the central aperture 24
of the lowermost tray 18 which rests on the plate 36. The
cover 16, on the other hand, is releasably secured to a
laterally outwardly extending flange 40 by means of a bolt
and nut arrangement 42. The outlet 32 is located centrally
of the cover 16 above the uppermost tray 20.
An outer concentric wall 44 spacedly surrounds the
container 12 so as to define therebetween an annular chamber
46 adapted to contain a thermostatic fluid for maintainina
the liquid inside the container at a substantially constant
temperature. The chamber 46 is provided with a lower inlet
48 and an upper outlet 50 for respectively receiving and
discharging the thermostatic fluid, thereby allowing the
fluid to circulate continuously through the chamber 46.
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In the experimental bioreactor 10 shown in
Fig. 1, a plurality of sampling tubes 52 are arranged at
predetermined locations along the length of the reactor,
each tube 52 extending through the outer wall 44 and
opening into the container 12. With these tubes 52,
samples can be taken and analyzed to determine the
conversion rate of the substrate being treated. An
lndustrial model, however, would not have any such sampl-
ing tubes.
Turning to Fig. 3 which schematically illus-
trates the liquid flow through the contaliner 12 from one
tray to another, where each tray 18,20 is seen supporting
a respective bed of microorganism cells 54, the apertures
24 and 26 of the trays 18 and 20 are arranged relative to
one another to cause the liquid to flow laterally across
the respective cell beds 54 of the trays as the liquid
flows from a lower tray to an upper tray. Moreover,
owing to the provision of a single central aperture 24 in
each tray 18 and of diametrically opposite apertures 26
in each tray 20, which are arranged on either side of the
central vertical axis 56 extending through the central
aperture 24, the liquid flows radially outwardly across
the respective cell bed 54 of each tray 18 as shown by
the arrows A, and then radially inwardly across the
respective cell bed 54 of each tray 20 as shown by the
arrows B. Such an arrangement prevents the cells 54
from being entrained by the liquid flow and thus enables
the cells to be retained inside the container 12.
Fig. 4 schematically shows the set-up of three
identical bioreactors 10 connected together for the bio-
chemical treatment of a liquid containing organic matter~
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The liquid to be treated which is contained in the feed
tank 58 provided with a sterile filter 60 to prevent
contamination of the iiquid by the ambient air is fed to
the inlet of the reactor ~o.-l via line 62 by means of
pump 64, after having first passed through a thermostatic
bath 66 containing water maintained at a constant tempe-
rature, for example 25C. me water of the bath 66 is
also fed via line 68 by means of pump 70 to the inlet of
the annular chamber 46 of reactor No. 1, the outlet of
which is connected via line 68a to the inlet of the
annular chamber 46 of reactor No. 2, which in turn has
its outlet connected via line 68b to the inlet of the
annular chamber 46 of reactor ~o. 3, such that the water
of the bath 66 is circulated through the chambers 46 of
all three reactors and is then returned to the bath via
! line 68c. The liquid to be treated flows through the
container 12 of reactor No. 1 from a lower to an upper
tray and radially across the respective cell beds of the
trays 18,20, where it reacts with the cells. The mixture
of gas and liquid which is produced as a result of thîs
reaction is discharged through the outlet of the reactor
and sent to a gas/liquid separator 72 which separates
the gas from the liquid. me gas is vented off via
line 74 and the separated liquid is fed via line 62a to
the inlet of the next reactor No. 2, for further treat-
ment. m is operation is repeated twice by means of
- reactors Nos, 2 and 3 which are connected together via
line 62b, in order to ensure a substantially complete
conversion of the organic matter contained in the liquid
which is finally discharged via line 62c.
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It should be noted that the gas which is
liberated at the surfaces of the cells as a result of
the reaction creates a turbulence inside the container
12 of the reactor 10, between the trays 18 and 20, and
this turbulence may cause some of the cells to be
en~rained by the liquid flow. However, since the reac-
tion has greatly diminished in the reactor ~o. 3 and has
completely stopped in the last upper trays thereof, any
entrained cells will collect in reactor ~o. 3 which will
thus act as a cell collector. Therefore, before starting
a new cycle, the reactors can be repositioned so as to
restore the cell balance, that is, reactor No. 3 becomes
No. 1, reactor No. 1 becomes ~o. 2 and reactor ~o. 2
becomes ~o. 3. In the following cycle, reactor ~o. 2
then becomes No. l, reactor No. 3 becomes No. 2 and
reactor No. 1 becomes ~o. 3.
The following non-limiting examples further
illustrate the invention.
EXAMPLE 1
- An aqueous solution of fermentable sugars was
fermented at 25C using the system shown in Fig. 4. The
solution contained 5.3 g/l galactose, 5.3 g/l glucose and
19.4 g/l mannose. Each reactor 10 had a height of 36 cm,
an internal diameter of 6.4 cm and a volume of about 1
liter. The reactors were inoculated with 80 g/l of the
yeast ~ yces cerevisiae and were fed with the solu-
tion at a flow rate of 5 ml/min. ~s shown in Fig. 5, the
conversion of the sugars was substantially complete
after a residence time of S hours (curve A) with reactors
each containing 34 trays, and a residence time of 8 hours
(curve B) with reactors each containing i7 trays.
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This experiment was repeated with a bisulfite
liquor from the pulp and paper industry and essentially
the same results were obtained.
EXAMæLE _
- The system illustrated in Fig. 4 was also used
- .
for the biotreatment of an effluent from a cheese plant
- to reduce the chemical oxygen demand (C.O.D.) and
. . to produce me thane .
An anae'robic biomass, from industrial source
was used to effect the biodegradation. The reactors were
inoculated with 45 g/l of volatile solids- in suspension-.-
The total volume of the reactors was about 3 liters. The
effluent tested had the following,composition, additives
having been added to increase the alkalinity and to
supplement the nitrogen and phosphorus sources:
lactoserum : 1.5 g/l
~H4HC03 : 0.0949 g/l
- ~aHCO3 : 1.7778 g/l
- KHCO3 : 1.7778 g/l
- (NH4)2 SO4 : 0.556 g/l
~ KH2PO4 : 0.0205 g/l
- Yeast extract : 0.0111 g/l
- pH : 8.49
- alkalinity : 3900 mg/l CaC03
The reaction was carried out at 30C with a
flow rate of 4.34 l/day, corresponding to a residence
time of 16.7 hours.
The pH change as a function of the residence
time was the following:
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Residence Time (h)
0 8.49
0.9 7.17
4.6 7.23 .
6.5 7.14
. 10.2 7,28
12.0 : 7.31
15.8 7.,41
The average quantity of gases produced (CH4 and
10 C02) per day was about 2. 35 liters (STP), the average
proportion of methane being 73%. The production of
methane per kg of C.O.D. removed was 0.3 m
The removal of the C O.D. as a function of the
residence time which is reported in Fig. 6 was the
15 following: ~
Residence Time (h) C.O.D.
Imq/l)
0 1492
0.9 906
4.6 431
6.5 376
10.2 158
12.6 130
15.8 .
As it is apparent from Fig. 6, the invention
enables to reduce the C.O.D. by 93% and 71% of this
reduction occurs in the first 4.6 hours of treatment.
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